1. Field of the Invention
The present invention relates to an inkjet printer and a bubble reducing method for an ink jet printer that perform printing with use of a printing head in which ejection ports ejecting ink are arrayed.
2. Description of the Related Art
There is known an inkjet printer that supplies ink from an ink tank containing the ink to a printing head through an ink supply path, and ejects the ink from a nozzle arranged in the printing head to perform printing. In the inkjet printer, a bubble accumulates in the ink supply path or printing head, which may cause the occurrence of improper ejection in the printing head.
As one of methods for removing the bubble, a cleaning process that seals a formation surface of an ejection port of the nozzle of the printing head by a capping unit, and sucks and discharges the bubble mixed in the ink, together with the ink, from the ejection port by negative pressure from a suction pump is performed.
In general, in the middle of the ink flow path to the printing head, in order to prevent a foreign substance mixed in the ink supplied from the ink tank from approaching, a filter member is arranged. A bubble in the ink flow path on an upstream side (ink tank side) of the filter member can be discharged by generating fast flow of the ink at the time of the cleaning process. As the cleaning process that generates the fast ink flow as described, a cleaning process called choke cleaning is proposed.
In the choke cleaning, first performed is an operation that, at the time of starting to suck ink through a capping unit, closes an on/off valve (hereinafter referred to as a choke valve) present between an ink tank and a filter to bring an inside of the capping unit to a predetermined negative pressure, and then opens the choke valve. According to this, a flow speed of the ink in the printing head can be instantaneously increased, and thereby the bubble on the upstream side of the filter member can be passed through the filter member and discharged outside.
However, in the case of performing the above choke suction, there is a problem that the negative pressure accumulated on the capping unit side is also instantaneously reduced by the ink flowing in, which may stop short of sufficiently discharging the bubble. In this case, the bubble remains in the ink flow path in the printing head, which may cause improper ejection.
As the choke cleaning for improving the above problem, Japanese Patent Laid-Open No. 2007-98959 proposes a sequence that, at the time of performing the choke cleaning, depressurizes a flow path, and even after opening the choke valve, keeps performing the suction without stopping the suction pump. This is intended to discharge the bubble from the printing head together with the continuous ink flow.
However, in the choke cleaning having the sequence disclosed in Japanese Patent Laid-Open No. 2007-98959, in the process from opening the choke valve to stopping the suction pump, as long as the bubble is present on the upstream side of the filter, the bubble may pass through the filter to flow into the printing head. That is, as long as the suction operation is not continued until the bubble on the upstream side of the filter is completely eliminated, the bubble may be mixed into the printing head to cause the improper ejection. For this reason, in the case of attempting to completely eliminate the bubble on the upstream side of the filter, there is a problem that a large amount of ink should be consumed, which increases running cost.